Summary. Cryo-electron microscopy offers a unique and practical method to determine the antigenic potential of influenza virus vaccine strains. High resolution electron micrographs with 3D reconstruction allow the viability of the virus particles to be quickly determined allowing for high-yield antigen production during the manufacturing process. Analysis of the virus surface directly demonstrates the density of the virus proteins that constitute the major antigenic element.
Advantages. Cryo-electron microscopy allows:
Influenza epidemiology and health threat. The influenza virus causes epidemics and every few decades is responsible for pandemics. According to data from the World Health Organization (WHO) flu results in an estimated 250,000 to 500,000 deaths and 3-5 million cases of severe illness per year worldwide. Influenza is an acute respiratory disease of significant mortality. Its symptoms include high fever, prostration, malaise and inflammation of the respiratory tract. Influenza viruses (of the orthomyxoviridae family) are membrane enveloped negative stranded RNA particles. The influenza A viruses are the most important human pathogen responsible for epidemics and pandemics. Influenza B is able to cause significant epidemics but not pandemics while influenza C are endemic and cause a milder respiratory disease.
Technology. Cryo-electron microscopy technology produces extremely high-resolution electron micrographs at near-molecular size. Samples are immobilized in vitrified ice and the native conformation of virus particles and their structural elements is maintained. Projection images easily resolve the viral surface elements (Figure 1, arrows). Electroncryo tomography technology can resolve viral particles at greater than 10 nm resolution and reconstruction software produces accurate 3D reconstruction images. High-yield influenza recombinants approach spherical shape that is easily demonstrated in the reconstructions (Figure 2).